As people age, it often gets harder for them to understand speech in noisy environments, causing them to participate less in social activities and reducing their quality of life. A key to helping older adults improve their quality of life is o improve their ability to understand speech in noise. To do this, researchers first need to determine why this functional decrease occurs. It is possible that the function of the inner ear decreases with age, even when hearing ability in quiet is not greatly affected. Two-tone suppression is a sensitive measure of inner ear health. Suppression may enhance aspects of speech, making it stand out better in noise. There is contradictory evidence about whether suppression decreases with age, whether it differs between men and women, and how it relates to speech understanding in noise. In young adults, suppression can decrease with long maskers that elicit a feedback loop that reduces amplification, or gain, in the cochlea, but this is has no been tested in older adults. This gain reduction may also be critical for speech understanding in noise. The purpose of this study is to determine age effects and sex differences on suppression magnitude and gain reduction, and how suppression and gain reduction magnitudes relate to the ability to understand speech in noise. Younger adults (age 20-30) and older adults (age 65+) with normal hearing will be tested. Magnitudes of suppression and gain reduction will be measured by obtaining thresholds to a short tone in the presence of masking noise of varying durations and frequencies. In order to disentangle the effects of suppression, the gain-reducing feedback loop, and increased age, suppression will be systematically explored using a phenomenological model of the auditory system. This will provide a much-needed model of the aging auditory system. Participants will also distinguish between different consonant-vowel (CV) words in quiet and in noise. Each person's magnitude of suppression and gain reduction will be compared to their ability to understand these CV words in noise. Also, percent correct and consonant confusions will be compared between the groups. This approach is innovative in that it addresses both suppression and gain reduction in men and women of ages across the lifespan. The use of the model will provide an even deeper understanding of suppression, the gain-reducing feedback loop, and how these measures are affected by increasing age. The new knowledge about gain reduction can lead to improved hearing aid strategies to improve speech understanding in noise for older adults, which can also improve their quality of life.